Graphic data transcription system

ABSTRACT

Graphic data transcription apparatus comprising a writing plate made of an electrically resisting medium and having a given shape, two sets of terminals arranged along the periphery of said plate, means for alternately and rhythmically applying to one and the other of said sets biasing voltages to sequentially produce at a given frequency two mutually orthogonal electric fields in said medium, the terminals in each one of said sets being alternately interconnected and insulated from each other, a conductive point probe in bearing contact with and movable on the writing plate surface, and means for using the voltage alternately developed between said probe and a point at a fixed reference potential to visually reproduce on a receiver the geometric track followed by said probe on said surface. In the case of a rectangular writing plate, the ratio of the width of the terminals in each one of said sets to their mutual spacing is preferably comprised between one and two.

United States Patent l 72] Inventors Lucien C. Malavard Paris; Pierre M. Marty, Verrieres-leBuisson, both of France [2]] Appl. No. 888,381 [22] Filed Dec. 29, 1969 [45] Patented Jan. 4, 1972 [73] Assignee Agence Nationale de Valorisation de la Recherche A.N.V.A.R. Puteaux, France [32] Priority Dec. 31, 1968 l 3 3 France [31 182840 [54] GRAPHIC DATA TRANSCRIPTION SYSTEM 5 Claims, 13 Drawing Figs. [52] 11.8.0 178/18 [5 l int. Cl H04n 1/00 [50] Field ofSeareh 178/18, 19, 20

[56] References Cited UNITED STATES PATENTS 3,522,664 8/1970 Lambrightet a1. 35/8 2,704,305 3/1955 McLaughlin et a1 178/8 2,565,612 8/1951 Levin 178/19 FORElGN PATENTS 1,080,592 4/1960 Germany Primary Examiner-Kathleen H. Claffy Assistant Examiner-Horst F. Brauner Attorney-Littlepage, Quaintance, Wray & Aisenberg ABSTRACT: Graphic data transcription apparatus comprising a writing plate made of an electrically resisting medium and having a given shape, two sets of terminals arranged along the periphery of said plate, means for alternately and rhythmically applying to one and the other of said sets biasing voltages to sequentially produce at a given frequency two mutually orthogonal electric fields in said medium, the terminals in each one of said sets being alternately interconnected and insulated from each other, a conductive point probe in bearing contact with and movable on the writing plate surface, and means for using the voltage alternately developed between said probe and a point at a fixed reference potential to visually reproduce on a receiver the geometric track followed by said probe on said surface. In the case of a rectangular writing plate, the ratio of the width of the terminals in each one of said sets to their mutual spacing is preferably comprised between one and two.

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PATENTEB JAN 41972 SHEET 9 [1F 9 1 GRAPHIC DATA TRANSCRIPTION SYSTEM This invention relates to a graphic data transcription system, more particularly of the kind for tracing and copying signs such as alphanumeric characters, signatures and drawings and for transmitting and reproducing them at distance in analog form or after digital conversion. The system according to the invention is of use inter alia as a peripheral input facility for a digital computer or as a display table and can form therewith a two-way or multiway communication system.

The apparatus according to the invention comprises a writing plate made of an electrically resistant material having a given shape, two pairs of equipotential electrodes each comprising two elements, at least one series of conductive terminals which are not connected to one another and which are each in contact with the writing plate and which are distributed along a line near the writing-plate periphery; means for applying a constant biasing voltage alternately and periodically at a selected repetition frequency between the two elements of one and the other electrode pair, such voltage raising the potential of each of the two elements to a given value relatively to a reference-potential point; switching and connection means controlled by a control signal generator to alternately and periodically connect at least some of such terminals to the electrode pairs and to produce an electric field on the surface of the writing plate, the or each series of terminals being so disposed that electric fields produced thereby on the writingplate surface when the or each series of terminals is consecutively connected to one and the other of said electrode pairs are at right angles to one another; a conductive point probe in bearing contact with and movable on the writing-plate surface; and means which use the voltages developed alternately at such frequency between the probe and the reference-potential point to reproduce visually on a receiver the geometric track followed by the probe in its movement on the writingplate surface, on the basis of the values of the alternately produced voltages and respectively representing the analog values of the two components of selected geometric coordinate system on the writing-plate surface.

In the apparatus according to the invention, the terminal se' ries are so arranged that the ratio of terminal width measured along the line portion along which the terminals are disposed to the space between two consecutive terminals is between one and three; and the resistant plate is in contact with each terminal only by way of a very small fraction of the terminal surface.

The reasons for the foregoing are the experimental findings that if the terminal width-to-spacing ratio is too small, distribution over the plate surface of the electric field produced by the terminals which are biased at any particular time is irregular and impairs accurate analog representation of the coordinates by the electrical potential of the probe. However, if the ratio is too large, the result of inadequate spacing for those terminals not receiving a bias voltage at a given time is that such unbiased terminals behave somewhat like a continuous conductive member and greatly disturb the electric field produced on the plate surface by those terminals which are biased at that particular time.

In a first form of the invention, the operative surface of the resistant plate is in shape rectangular; and four series of terminals are disposed one along each side, of the rectangular outline of the plate, each pair of such series disposed along opposite sides of said outline also forming one of the electrode pairs when the terminals thereof are respectively linked by direct connections to two points between which said biasing voltage is applied. The coordinates used in this case are Cartesian coordinates.

In a second form of the invention, also using Cartesian coordinates, the operative surface of the resistant plate is in shape circular and all the said terminals are disposed on a circle forming the outline of the operative surface, the two elements of each electrode pair which are brought alternately to different potentials consisting of two further series of terminals disposed along straight lines around the circularly arranged terminals and connected alternately to all latter the terminals so as to impart to each one thereof a potential which is a function of the angular position of such terminal, the connection between the circularly arranged and the said further terminals being effected through the agency of resistances of appropriate values energized from the electrodes, the distribution of the terminals at any particular time differing according as one or the other of the electrode pairs is the one which is biased at that particular time.

In an alternative of the second form of the invention, the various potentials required for the terminals are produced by a system comprising two auxiliary electrode pairs each comprising a series of terminals disposed on a fraction of a circle and alternately energized at a constant potential, an auxiliary system of terminals arranged in a circle, an auxiliary resistant plate in electrical contact with the two auxiliary pairs and with the last-mentioned system, and a direct connection between each of the terminals of the auxiliary system and a corresponding one of the terminals arranged in a circle on the outline of the resistant plate.

In another form of the invention, using polar coordinates, one of the electrode pairs comprises two series of terminals disposed on two circle radii, and the other electrode pair comprises in the case of one of its elements terminals distributed around the periphery of such circle and in the case of the other element a terminal disposed at the center of such circle, the last-mentioned terminal possibly being divided into a number of smaller terminals. In the latter case, the said terminals also constitute the peripheral series of terminals which are used to produce the desired electric fields on the surface of the resistive plate.

In all cases, the terminals which at any particular time are connected to a single biased electrode are themselves electrically interconnected, but the terminals connected at that particular time to the same unbiased electrode are isolated from one another through the agency of appropriate switching means controlled by the control signal generator.

The invention will be more clearly understood from the following detailed description and accompanying drawings wherein:

FIG. ll shows the basic circuit diagram of an apparatus according to the invention, for the case where the writing plate is rectangular, the coordinates are Cartesian and the switching means are electromechanical relays;

FIGS. 2 and 3 are diagrams showing the effect of the terminal width-to-spacing ratio on the shape of the electric fields produced in the resistant material of the writing plate;

FIGS. 3a, 3b, 3c and 3d are diagrams showing, in the case of a rectangular writing plate, the influence of the relative dimensions of terminals and spacings on current line distortion;

FIG. 4 is a perspective view of writing-plate construction when the plate is used for copying;

FIG. 5 shows some of the circuit diagram of the facility according to the invention when the switching means are transistors;

FIG. 6 shows electrical means for applying to the terminals in contact with the writing plate voltages distributed in accordance with an appropriate law, in the case in which the writing plate is circular and the coordinates used are Cartesian;

FIG. 7 shows a first embodiment of the invention which a circular writing plate, in the case in which polar coordinates are used;

FIG. 8 shows a second embodiment of the invention with a circular writing plate, in the case in which the coordinates used are Cartesian, with an auxiliary system for applying appropriately distributed voltages to the terminals around the plate periphery, and

FIG. 9 shows a constructional variant of the writing device wherein the probe is not a pencil or tip but a flexible metallized strip or foil or the like stretched over the writing plate.

Referring first to FIG. 1, there can be seen a writing plate 2 and terminals. In practice a relatively large number of terminals are provided, but to simplify the drawing the number of terminals shown therein is reduced. The terminals along the two long or major sides of the plate have the references 301 to 320 and 321 to 340, while the terminals along the two short sides have the references 341 to 355 and 361 to 375.

Terminals 301 to 320 are connected to the positive side of a DC supply via contacts of a relay 7. Similarly, the terminals 321 to 340, 341 to 355 and 361 to 375 are connected to the negative, positive and negative side respectively, of the DC supply via contacts of relays 8, 9, 10. Only four relays 7-10 are shown; in practice, a sufficient number of relays is provided for them to have enough contacts to energize all the aforementioned terminals. A generator 11 producing periodic control signals controls the relays 7, 8, on the one hand, and the relays 9, 10, on the other hand, alternately.

Associated with plate 2 is a probe 12 in the form of a pen or pencil or the like which has e.g., a graphite tip and with which the operator writes on the plate 2. Consecutive signal pairs are collected between probe 12 and a reference-potential point; the amplitudes of such signal pairs respectively measure the abscissa and ordinate of the contact point, which is better defined in proportion as the control signal distribution frequency is higher relatively to the speed of writing. In practice the last-mentioned frequency can be e.g. 1,000 hertz. Probe 12 is connected by a flexible wire to a series-parallel converter 13 serving to separate abscissa signals from ordinate signals and to delay one of the two signal groups relatively to the other by half the signal repetition period. Converter 13 therefore delivers pairs of simultaneous signals respectively measuring the abscissa and ordinate of a point of the graphic data being written or copied.

The abscissa and ordinate signal trains are used differently according as it is required to directly display the data or convert the same into digital indications. For display, the trains go to a low-pass filter 14 for conversion into an analog signal, and the resulting signals are applied to the horizontal and vertical deflecting plates of a display tube (oscilloscope) 15. For digital conversion, the trains go to a converter for converting amplitude-modulated signals into coded groups of binary signals (PCM) 16. The binary signals are registered in a store 17 and, if required, processed by a data processing system 22.

If the number of terminals along any one side of the writing plate is greater than the maximum number of contacts of a single relay, the terminals can of course be divided into groups which are brought to the appropriate potentials by way of the contacts of a number of parallel-energized relays.

Referring now to FIG. 2, a part of the rectangular plate 2 shown in FIG. 1 can be seen in greater detail. The hatched area of FIG. 2 represents the resistive layer forming the writing plate 2, and the terminals 319, 320 and 341-343 perform the same functions as the terminals of like references in FIG. 1.

As can be seen in FIG. 2, where it is assumed that that ratio of the width of a single terminal to the space between two consecutive terminals is about 3, the terminals (341, 342, 343) or (319, 320) make contact with the plate 2 over only a very small proportion of terminal surface. The advantage of this feature is that when e.g. the terminals 341-343 are not connected to a bias voltage source, there is a relatively high resistance between any two adjacent terminals, but when those same terminals are connected to the bias source, the last-mentioned resistance has no effect, all things being as if the terminals concerned were interconnected by direct connections.

Referring now to FIG. 3, the left-hand portion shows the distortion of the current lines 401-403 extending from a top terminal, as 341-343 (FIG. 1), to a bottom terminal 361-363, on the assumption that both such terminals are those energized at the considered time and are disposed opposite one another. As can be seen in the left-hand part of FIG. 3, where the assumption has been made that terminal width is reduced relatively to between-terminals spacing, the current lines tend to be concentrated near straight lines interconnecting the centers of facing terminals 341 and 361 or 342 and 362, and to thin out in the spaces between such straight lines. On the other hand, due to the high resistance between the terminals 319 and 320, which are assumed not to be energized at this particular time, only a relatively few current lines are deflected towards the latter terminals, and there is but very little distortion of the current lines extending between pairs of energized terminals, as (341,461), etc.

In the right-hand part of F IG. 3, however, it is assumed that the various terminals 341-343, 361-363 and 301-320 have a high width-to-space ratio. Consequently, distribution of current lines 501-505 between pairs of energized terminals is substantially uniform in the central part of the writing plate, although, as can be seen in the right-hand part of FIG. 3, there is considerable distortion of current lines, as 541, 561, in the plate parts near deenergized terminals, as 301 and 320, because of the low resistance between them which results from their reduced spacing and the resulting overall low resistance of the path 301 to 320.

For a satisfactory practical result, a compromise must be made between the extreme conditions shown in the left-hand and right-hand parts respectively of FIG. 3, and a compromise of this kind has led to the value previously given of between 1 and 3 for the terminal width-to-spacing ratio.

In the case of a rectangular writing plate, it has been found that the optimal value of the latter ratio is comprised between 1 and 2.

FIGS. 3a, 3b, 3c, 3d show the behavior of the current lines inside an elongated band of the resisting plate perpendicular to one of the edges thereof and having a width equal to the half-pitch (p/2) of the terminals (that is equal to the half-sum of the width m of a terminal and of that of a spacing between two contiguous terminals). This band is limited by the perpendicular line y'y' to the said edge at the middle point a of the width of the considered terminal and the perpendicular line y 'y" to the same edge at the middle of a spacing contiguous to that terminal. In FIGS. 3a to 3d, the parts M and I shown along the axis xx respectively represent the half of a metallic (or metallized) terminal and the insulating half-spacing contiguous thereto.

The curves shown in FIGS. 3a to 3d are the loci of the points of the resisting plate at which a given angle 0 exists between the electric field (and, consequently, the current lines) and an ideal direction perpendicular to the edge of the plate, the latter edge being taken as the x-x axis in all of the latter FIGS. Along the yy' and y"-y" axes, the angle 0 is zero, by reason of symmetry. Along the part I of the x-x axis, 0 is equal to degrees, since the electric field lines are perpendicular to the interface between the insulating part I and the half-terminal M. In each of FIGS. 3a to 3d are shown the various curves corresponding to 0 0.5; 2; 5; 10; 2O; 40; 50 and 70 degrees The region of the plate for which the curves corresponding to an angle 9 having a given, nonzero value is a region in which the field lines are not parallel to each other. This region may be considered as all the more disturbed" that 0 has a lower value. It may be conventionally admitted, for instance, that the nonhomogeneous nature of the field makes the disturbed region useless for graphic transcription if the angle 0 exceeds 3 degrees. The magnitude of the projection on axes y-y' and y"y" of the maximum ordinate of the curve for which 0 equals 3 degrees then may be conventionally taken as a measure of the height h of the disturbed region.

In FIGS. 3a, 3b, and 30, it has been assumed that the resisting plate extends to infinity in the x-xdirection; the ratio (m/p) of the width m of a terminal to the above-defined pitch p has been successively given the values 0.5 (FIG. 3a), 0.7 (FIG. 3b) and 0.25 (FIG. 3c). In FIGS. 3a to 30 it may be seen that h is smaller in the case of FIG. 312 than in that of any other figure. Consequently, the best result would be obtained by taking (m/p) equal to 0.75 if account had not to be taken of the influence of the parallel to y-yterminal rows at both ends of the plate in the x x direction.

In FIG. 3d due account has been taken of the latter in fluence. The height h of the disturbed region then takes its minimum value for (m/p) equal to 0.57 The latter value is the optimal one, but, in practice, a value of m/p between 0.5 and 0.65 may be adopted. The latter value thus corresponds, for the ratio of the width of a terminal to that of a spacing between two contiguous terminals, to a value comprised between I and 2.

Referring now to FIG. 4, showing more particularly an em bodiment of a part of the apparatus according to the invention when the same is to be used for copying, the apparatus comprises an illuminated base 1 adapted to receive a sheet of paper comprising graphic data to be copied, if the apparatus is to be used for copying. Articulated to base 1 is a transparent plate 2 on which a thin conductive surface layer is deposited. The resistance per square" (equal to the quotient of resistivity divided by thickness) of the layer is between 100 and 800 ohms. In the present day state of the art, the transparency of the coated plate increases with the resistance per square; for instance, plates having resistances per square of 170,300 and 800 ohms have transparencies of 45, 50 and 60 percent respectively. A plate having a resistance of e.g. 800 ohms can be chosen.

In cases where the writing plate is placed on top of a cathode ray display tube, either the transparent plate can be applied directly to the outside surface of the tube screen or the resistant layer can be deposited thereon directly.

Disposed along each side of plate 2 are discrete printed terminals 3 into which connectors 4 can be plugged; only one connector 4 is shown in FIG. 4. The rectangular electric fields are applied to the writing plate via the terminals 3. Preferably, the spacing between adjacent terminals is comprised between one-third of the width of a single terminal and the latter width. A framelike cover 5 can be folded down onto the writing plate and serves to bound the area available for writing and to protect the terminals and connectors.

Referring now to FIG. 6 (Cartesian coordinates), it has been assumed that the writing plate is circular and is e.g. the screen of a cathode ray tube, the screen outer surface being made appropriately conductive. In this case the screen is mounted in a square frame 18 placed around the circular writing plate 19. The frame 18 and 19 each have peripheral terminals, 3 and 34 respectively. Inserted between two terminals 3 and 34 of the same abscissa (r cos 0) or of the same ordinate r sin 0 (see FIG. 6) are resistances 20, 21 having the values:

R (I cos 6) and R (I sin 0), R denoting an appropriate resistance. The frame 18 can be omitted and the abscissa resistances 20 can be directly connected to the contacts of the relays 7 and 8 of FIG. I, while the ordinate resistances 21 can be directly connected to the contacts of the relays 9, 10, of FIG. 1. The opposite sides of the frame 18 serve as pairs of constant-potential electrodes from which the terminals, as

34, are energized.

Referring to FIG. 7 (polar coordinates), there are two fields at right angles to one another, one field being tangential and the other radial. The tangential-field terminals 31, 32 are disposed along two radii. Of the radial-field terminals 33, 34, 33 is disposed at the center of plate I9 and the other terminals 34 are disposed around the plate periphery. Preferably, the terminals 31-33 are placed on the back of the plate so as not to impede writing and are connected to the covering conductive layer be metal lead-throughs. That part of the plate which is disposed between the terminal rows 31 and 32 is insulating. The terminals 31-34 are connected to appropriate sides of the power supply by the contacts of relays 27-30 performing the same function as the relays 7-10 of FIG. 1.

Referring to FIG. 8 (Cartesian coordinates), the circular writing plate 19 has peripheral terminals 34, for instance, I20 terminals 34. Associated with plate 19 is an auxiliary resistant plate 35 which is not used for writing and which has peripheral terminals 36 also to the number of I20, and four groups of terminals 37-40 disposed on circle sectors all passing through the center of plate 35 and offset from one another by 90 degrees. These four circle sectors are the transformed curves by geometric inversion of the sides of an ideal square circumscribed around the circular plate 19. The terminals 36 are connected to the respective terminals 34 of like positions by resistance-free connections. The terminal groups (37, 38), (39, 40) are connected to the poles of a DC power supply in exactly the same way as are the terminal groups (301-320 ,321-340) and (341-355, 361-365) of FIG. I.

A result of the known properties of potential in respect of geometric inversion in a plane is that the application of constant potentials to the circle sectors on which the terminal groups (37, 38), (39, 40) are disposed produces the same potential distribution along the circle containing the peripheral terminals 36 as the potential distribution obtainable by the application of a constant potential to the sides of a square circumscribed about the last-mentioned circle. Consequently, the potential distribution along such peripheral terminals is the same as in the case of the circle with the terminals 34 in FIG. 6.

In the previous drawings, the potentials have been applied to the terminals, and the same have been connected and isolated, by means of relays. FIG. 5 shows how this feature can be provided by electronic ways and means and discloses an electronic relay of a kind such that the controlled circuit is in the closed state when the control circuit is energized by way of 56, 57, whereas the controlled circuit is in the open state when the control circuit is not energized. This is an electronic relay equivalent to the electromechanical relays 7-10 of FIG. 1.

The connection point, equivalent to the contact of an electromechanical relay, is embodied by two transistors 41, 42, transistor 41 being of the PNP type and transistor 42 being of the NPN type; the emitters of both transistors are connected to terminal 43 and the collectors of both transistors are connected to terminal 44, the circuit which it is required to open and close also being connected thereto. Such circuit comprises terminal series 301-320 and 321-340, each series being connected to the terminals 44, 43 respectively via high resistances 60 and a battery 61. Depending on its state, a current either flows or does not flow through each transistor 41 or 42 in a particular direction. When the relay is in the closed state, one or other of the transistors 41, 4.2 is conductive in the direction of the current flowing in the circuit which it is required to switch. The circuit therefore operates irrespective of which way round the battery 61 is connected.

The emitters of transistors 41, 42 are biased via resistances 45, 46, and two diodes 58, 59 protect the transistors against reverse emitter-collector voltages.

The control circuit for the connection point is embodied by two transistors 47 48. Transistor 47 is an NPN transistor controlling the PNP-transistor 41, and transistor 48 is a PNP transistor controlling the NPN-transistor 42. Each control transistor 47, 48 controls via its collector the base of a connection transistor 41, 42 respectively via a respective resistance 49, 50 and a respective diode 51, 52, the latter providing reverse-voltage protection for the transistors 47, 48.

Input circuit 57 comprises a network 55 assumed, in the case shown in FIG. 5, to comprise just a single resistance whose ends 53, 54 are taken to the bases of the transistors 47 40 respectively.

Operation is as follows:

When the control current output by generator 11 is applied in the direction going from 56 to 57, a signal is produced at the ends 53, 54 of resistance 55 and the potential of terminal 53 is above the potential of terminal 54. The signal opens (renders conductive) the control transistors 47, 48 and-provided there is nothing to prevent current form flowing from the emitter to the collector in the transistor 40 and from the collector to the emitter in the transistor 47-collector currents flow. If the potential of point 43 is above the potential of point 54, a current flows through transistor 47 and the potential drop in resistance 45 opens (renders conductive) the connection transistor 41. However, the diodes 52, 59 prevent any current flow in transistor 48 and transistor 42 stays closed (nonconductive or cutoff). The controlled current flows through transistor 41.

lf the potential at the point 43 is below the potential at the point 53 (or at the point 54, since the potentials at the points 53 and 54 are very similar to one another), a current flows through transistor 48 and the potential drop in resistance 46 opens (renders conductive) the transistor 42. However, the diodes 51, 58 prevent any current flow in transistor 47 and transistor 41 stays cut off. The controlled current flows through transistor 42. When the control current is applied in the direction going from 57 to 56, the transistors 47, 48 and therefore the transistors 41, 42 remain cut off, as they also do in the absence of any application of control current to the electronic relay.

It has been assumed in the foregoing that the pencil or pen or the like leaves no trace on the surface of a resistant plate. If it is required to retain such a trace, a special pencil or pen or the like can be used which has a conductive lead leaving a trace on the plate of sufficiently high resistance not to disturb the electric fields. Another possibility is to use a conventional felt pen using an insulating ink and whose felt tip comprises a metal wire, e.g. a gold wire.

FIG. 9 refers to the case in which the pencil or pen or the like 12 of FIG. 1 is entirely absent for specific purposes. In this case, the writing plate 2 covered with the resistant layer 23 has placed on it a thin flexible transparent sheet or foil or the like 25 which, as a reference 24 indicates, is conductive on its inside surface and which serves as pencil or pen or the like. The sheet 25 can be made e.g. of a polyester known under the trade name of Mylar. Sheet 25 is stretched parallel to the plate 2 and does not contact the same when in the inoperative state. The operator produces contact between layer 23 and layer 24 just by pressing with the finger or any article on sheet 25, the contact being passed to the series-parallel converter 13 shown in FIG. 1.

The facility according to the invention has many uses which will be immediately apparent to the man of the art and which relate in general to sequential transmission of the coordinates of the points of any set of graphic data, their display, digitalization, storage and processing as information data.

Only rectangular and circular display and copying plates have been described in detail, but the invention is of course of use for plates of any shape.

It has been assumed in the foregoing that the electric fields are produced by equipotential electrodes. Different potential patterns could of course be used for the outlines of the writing plate; for instance, a resistance calculated to provide the required law or pattern could be inserted in the energization circuit for each terminal Also, the different potential distribution patterns required for the terminals around the plate periphery can be produced by a digital computer to which a corresponding program is supplied and which has an appropriate number of outputs, each output having if necessary a decoder for converting the coded value of a voltage into an analog value. In this case the clock associated with the computer can also serve as the control signal generator 11 of FIG. 1.

What we claim is:

l. A graphic data transcription apparatus comprising a writing plate made of an electrically resistant material having a given shape, two pairs of equipotential electrodes each comprising two elements, at least one series of peripheral conductive terminals spaced from one another and each in contact with the writing plate and distributed along a line near the writing-plate periphery; means for applying a constant biasing voltage supplied between two fixed potential points alternately and periodically at a selected repetition frequency between the two elements of one and the other electrode pair, such voltage raising the potential of each of said two elements to a given value relatively to a reference-potential point; switching and connecting means controlled by a control signal generator to alternately and periodically connect at least part of such terminals to said electrode pairs and to produce an electric field on the surface of the writing plate, said series of terminals and said connection means being so disposed that electric fields produced thereby on the writing-plate surface when said series of terminals are consecutively connected to one and the other of said electrode pairs are at right angles to one another; a conductive point probe in bearing contact with and movable on the writing-plate surface; and means using the voltages developed alternately at said frequency between said probe and said reference-potential point to reproduce visually on a receiver the geometric track followed by the probe in its movement on the writingplate surface, on the basis of the values of the alternately produced voltages and respectively representing the analog values of the two components of a selected geometric coordinates system on the writing-plate surface, said peripheral terminal series being so arranged that the ratio of terminal width measured along the line portion along which said terminals are disposed to the spacing between two consecutive terminals is comprised between one and three; and the resistant plate being in contact with each terminal only by way of a very small fraction of the latter terminal surface.

2. Apparatus as set forth in claim 1, in which the operative surface of the resistant plate is of rectangular shape and in which two series of terminals are respectively disposed one along each pair of opposite sides of the rectangular periphery of the plate, each such series also forming one of the electrode pairs, when all terminals thereof are connected by direct connections to one of said fixed potential points.

3. Apparatus as set forth in claim 1, in which the operative surface of the resistant plate is of circular shape and in which all the peripheral terminals are disposed on a circle forming the outline of theoperative surface, the two elements of each electrode pair between which said constant biasing voltage is applied being composed of sets of terminals arranged along straight lines disposed around said circle and being connected alternately to all the terminals so as to impart to each terminal a potential which is a function of the angular position of such terminal, through the agency of resistors of appropriate values energized from said electrodes, the distribution of the said resistors at any particular time differing according to which of the electrode pairs is the one which is biased at said particular time.

4. Apparatus as set forth in claim 3, in which the various potentials required for the peripheral terminals are produced by a device comprising two auxiliary electrode pairs each comprising a further series of terminals disposed on a fraction of a circle and energized alternately at a constant potential, an auxiliary system of terminals arranged in a circle, an auxiliary resistant plate in electrical contact with the two auxiliary pairs and with said auxiliary system, and a direct connection between each of said auxiliary system and a corresponding one of the peripheral terminals arranged in a circle on the outline of the resistant plate.

5. Apparatus as set forth in claim 1, using polar coordinates, in which one of the electrode pairs consists of two further series of terminals disposed on two radii of a circle and the other electrode pair comprises as one of its elements terminals dis tributed around the periphery of such circle and constituting at the same time said peripheral terminals and as its other element a terminal disposed at the center of said circle.

UNITED STATES PATENT oTTTcr CERTIFICATE OF CCRRECTlON- Patent No. 3,632,874 Dated January 4th, 1972 In (s) LUCIEN C. MALAVARD and PIERRE M. MARTY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1', line 41, "dinate system" should read -dinates system-m Column 4, line 35, "point a of the" should read -point of the--; line 56, "nonzero" should read --non-zero-; line 60, "nonhomogeneous" should read --n.on homogeneous-; line 67, "x xdirection" should read -x x direction-;

line 69, "0.7" should read --0.75--; line 74, "y' y'terminal" should read --y' y' terminal--. Column 5, line 18, "present day" should read -present day-; line 20, "170,300" should read -l70, 300-.-; line 34, "framelike" should read -frame-like; line 60, "33" should read -terminal 33--. Column 6, line 51, "NPN-transistor" should read --NPN transistor; line 66, "form" should read -from-. Column 8, line 56, "between each of said" should read ---between each of the terminals of said-.

Signed and sealed this 22nd day of August 1972.

(SEAL) Attest:

EDWARD I LFLETGHEflJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69] USCOMM-DC 6O376-P59 U.S, GOVERNMENT HUNTING OFFICE: 1969 O-366334 

1. A graphic data transcription apparatus comprising a writing plate made of an electrically resistant material having a given shape, two pairs of equipotential electrodes each comprising two elements, at least one series of peripheral conductive terminals spaced from one another and each in contact with the writing plate and distributed along a line near the writing-plate periphery; means for applying a constant biasing voltage supplied between two fixed potential points alternately and periodically at a selected repetition frequency between the two elements of one and the other electrode pair, such voltage raising the potential of each of said two elements to a given value relatively to a reference-potential point; switching and connecting means controLled by a control signal generator to alternately and periodically connect at least part of such terminals to said electrode pairs and to produce an electric field on the surface of the writing plate, said series of terminals and said connection means being so disposed that electric fields produced thereby on the writing-plate surface when said series of terminals are consecutively connected to one and the other of said electrode pairs are at right angles to one another; a conductive point probe in bearing contact with and movable on the writing-plate surface; and means using the voltages developed alternately at said frequency between said probe and said reference-potential point to reproduce visually on a receiver the geometric track followed by the probe in its movement on the writing-plate surface, on the basis of the values of the alternately produced voltages and respectively representing the analog values of the two components of a selected geometric coordinates system on the writing-plate surface, said peripheral terminal series being so arranged that the ratio of terminal width measured along the line portion along which said terminals are disposed to the spacing between two consecutive terminals is comprised between one and three; and the resistant plate being in contact with each terminal only by way of a very small fraction of the latter terminal surface.
 2. Apparatus as set forth in claim 1, in which the operative surface of the resistant plate is of rectangular shape and in which two series of terminals are respectively disposed one along each pair of opposite sides of the rectangular periphery of the plate, each such series also forming one of the electrode pairs, when all terminals thereof are connected by direct connections to one of said fixed potential points.
 3. Apparatus as set forth in claim 1, in which the operative surface of the resistant plate is of circular shape and in which all the peripheral terminals are disposed on a circle forming the outline of the operative surface, the two elements of each electrode pair between which said constant biasing voltage is applied being composed of sets of terminals arranged along straight lines disposed around said circle and being connected alternately to all the terminals so as to impart to each terminal a potential which is a function of the angular position of such terminal, through the agency of resistors of appropriate values energized from said electrodes, the distribution of the said resistors at any particular time differing according to which of the electrode pairs is the one which is biased at said particular time.
 4. Apparatus as set forth in claim 3, in which the various potentials required for the peripheral terminals are produced by a device comprising two auxiliary electrode pairs each comprising a further series of terminals disposed on a fraction of a circle and energized alternately at a constant potential, an auxiliary system of terminals arranged in a circle, an auxiliary resistant plate in electrical contact with the two auxiliary pairs and with said auxiliary system, and a direct connection between each of the terminals of said auxiliary system and a corresponding one of the peripheral terminals arranged in a circle on the outline of the resistant plate.
 5. Apparatus as set forth in claim 1, using polar coordinates, in which one of the electrode pairs consists of two further series of terminals disposed on two radii of a circle and the other electrode pair comprises as one of its elements terminals distributed around the periphery of such circle and constituting at the same time said peripheral terminals and as its other element a terminal disposed at the center of said circle. 